Protection circuit of a transistor type direct current constant voltage device



J1me 1966 SHINICHIRO OGAWA ETAL 3,256,448

PROTECTION CIRCUIT OF A TRANSISTOR TYPE DIRECT CURRENT CONSTANT VOLTAGE DEVICE Filed Sept. 20, 1963 INVENTORS SHINICHIRO OGAWA YOTO O NAGAMATSU United States Patent Office 3,256,448 Patented June 14, 1966 3,256,448 PROTECTION CIRCUIT OF A TRANSISTOR TYPE DIRECT CURRENT CONSTANT VOLT- AGE DEVICE Shinichiro Ogawa and Kiyotomo Nagamatsu, Tokyo, Japan, assignors to Honeywell Inc., a corporation of Delaware Filed Sept. 20, 1963, Ser. No. 310,266 Claims priority, application Japan, Sept. 24, 1962, 37/ 40,982 1 Claim. (Cl. 307-885) This invention relates to a circuit protecting a transistor type direct current constant voltage device from an overcurrent by using a silicon controlled rectifier. In general, a short circuit of a load circuit and an overcurrent generated by an error of connection of a load exert significant ill influences on a transistor type constant voltage device.

The object of the present invention is to provide a nvel protection circuit in which an overcurrent is cut off from a load circuit instantaneously and automaticallyand said status is maintained unless a push-button switch S.W. on the output side of the transistor type direct current constant voltage device is pushed.

The object and advantage of this invention will become readily apparent from the following detailed description, in which:

The drawing is a view showing one embodiment of a protection circuit in accordance with this invention.

In the drawing, CVU is a transistor type direct current constant voltage device and E is a supply electric power source of said transistor type direct current constant voltage device CVU.

To positive terminal 1 on the output side of said transistor type direct current constant voltage .device CVU,

a load circuit in which a silicon control rectifier SCR is serially connected to a load RL and a by-pass circuit in which a silicon control rectifier SCR is connected serially to a bypass resistor RB of the load are connected.

An overcurrent detection circuit is inserted between said two circuits and the negative terminal on the output side of the transistor type direct current constant voltage device CVU consist of a voltage detection resistor R for gating SCR connected to the negative pole of SCR and a voltage detection circuit for gating SCR which is connected serially to a resistor R and to the negative pole of SCR at point 4, and said voltage detection circuit for gating said SCR consists of connecting a resistor R to the positive terminal of a reference electric power source E and by connecting parallelly a resistor R thereto.

The connection point of said resistor R and said resistor R is connected to the negative terminal 2 on the output side of the transistor type direct current constant voltage device CVU and the gate circuit of SCR and the gate circuit of said SCR consists of by connecting serially a gate protection resistor R and a silicon diode D The gate circuit of SCR consists of a gate protection resistor R and a silicon diode D and is connected to the negative terminal 3 of SCR C is a condenser; it is inserted between the anodes of SCR and SCR and assists the igni tion of a gate of SCR Next, we will explain the operation of the protection circuit of a transistor type direct current constant voltage device in accordanc with the present invention.

Supposing the electric current generated in the closed circuit formed by resistor R resistor R and reference electric current source E by only said reference electric current source E is I the voltage V between points 4 and 5 will be as follows:

It said voltage V is a suflicient value to ignite SCR' since a voltage is being applied to the gate circuit of SCR in the conducting direction, SCR is ignited and a load electric current I flows.

Said load electric current I flows through resistor R resistor R reference electric power source E and resistor R to the negative terminal on the output side of the transistor type direct current constant voltage device CVU.

Accordingly, due to said load electric current I the voltage V between the points 3 and 4 will have a value o'btained'by multiplying the sum of said load electric current Land the gate electric current of SCR by the resistor R and the voltage V between the points 4 and 5 will be as follows.

R3 V2413 m R2 It said load electric current I increases, the voltage V between the points 4 and 5 will further drop, and if said load electric current I exceeds.

If a resistor R is chosen in such manner that said voltage will become equal to an igniting voltage of are of SCR since a voltage in the conductive direction is being sent into the gate circuit of SCR it will be ignited instantaneously, the by-pass circuit will be made conductive and a by-pass electric current I which is a little smaller than the largest load electric current will flow. In that instance, since an extinction voltage of arc is being sent to SCR it will be assisted by condenser C and will ex tinct immediately and cut off the load circuit.

Like this, if said load electric current 1 reaches the largest load electric current I SCR will instantaneously ignite and complete the bypass circuit, extinct SCR; and cut off the load circuit, but, when this status is attained, the gate circuit of SCR is held in a negative voltage and will not be ignite-d again.

Also, though the gate .voltage V of SCR will almost become to be a zero voltage, as long as SCR does not ignite, SCR will never be extincted due to the operation of the condenser C and the characteristics of the silicon control rectifier.

Accordingly, as long as the transistor type direct current constant voltage device CVU is not cut 01f, it will never be switched from a by-pass circuit to a load circuit.

Incidentally, though it is desirable that a by-pass electric current I is equal to the largest rated load electric current I as far as the characteristics of a silicon control rectifier permits, it is economical that a bypass electric current I is smaller than the largest load electric current I10. I

As mentioned above, since the protection circuit of the transistor type direct current constant voltage device in accordance with the present invention will, if an overload electric current flows into a load circuit, cut off instantaneously the load electric current of the load circuit and switches to aby-pas-s circuit, it will protect safely the transistor type direct current constant voltage device 3 4 from an overload electric current generated by a shortmit current to flow in said load circuit between said circuit or an error of connection of load. terminals, 1

While a preferred embodiment of the present invention said first and second resistors being so connected as to is disclosed, it is recognized that the scope of the present apply a turn-off voltage to said first rectifier by way invention is not limited thereto and it is therefore inof said first gate circuit when the value of the current tended that the scope of the present invention be defined flowing in said load circuit exceeds a predetermined by the scope of the appended claim. value, and

What is claimed is: a second gate circuit including a second diode connect- A circuit for protecting a source of supply voltage from ing said first resistor between the gate and cathode excessive current flow comprising 10 of said second rectifier to apply thereto a turn-on a pair of terminals arranged to be connected to the outvoltage to render said second rectifier conductive put of the voltage source, when said current value exceeds said predetermined a load circuit including a load device, a first silicon value,

controlled rectifier, and first and second resistors conthe conduction of said second rectifier cooperating with nected in series between said terminals, 15 said turn-off voltage to render said first rectifier nona by-pass circuit including a by-pass resistor, a second conductive to reduce the fiow of current between said silicon controlled rectifier, and said second resistor terminals. connected in series between said terminals, a first gate circuit including a first diode connecting References Cited y the Examine! said first and second resistors between the gate and 20 UNITED STATES PATENTS cathod of said first rectifier, a source of reference voltage connected in parallel with 304O270 6/1962 Gutzwluer 307-885 X said second resistor and poled to apply a turn-on voltage to said first rectifier by Way of said first gate ARTHUR GAUSS Pumary Examiner circuit to render said first rectifier conductive to per- 25 LEE, Assistant Examine"- 

